The GammaMedica X-Spect, dual detector combined SPECT CT system utilizes two mosaic sodium-iodide crystal single photon radionuclide detectors mounted on a rotating gantry with a micro CT (for anatomic correlation and attenuation measurements), to record high resolution SPECT data on small animals. The radionuclide detectors have 1-mm resolution at the surface of a parallel hole collimator, and about 0.5mm when a 0.5mm pinhole collimator is employed. The GammaMedica microspect is the only commercially available system optimized for imaging small animals. The MicroSPECT system, specifically designed for rodent imaging, offers major advantages over the data that can be recorded with large field of view clinical instruments. The device offers superior spatial resolution, ease of use, and the ability to correlate the radionuclide data with high resolution computed tomography. Data recorded with this instrument will enhance the information obtained from ongoing NIH funded programs. Advantages of the X-SPECT device include: spatial resolution superior to microPET, ability to image multiple tracers of different energies simultaneously, incorporation of a user friendly system for image acquisition and analysis, and the relative advantage of using commercially available single-photon-emitting radionuclides for research studies. Eleven funded investigators will utilize the state-of-the-art capabilities offered by this instrument to enhance their work on studies of gene expression, tumor growth rate, apoptosis and targeted therapy. Using multiple labels, regional tumor perfusion, hormone receptor expression and apoptosis can be assessed simultaneously in the same animal, prior to, during, and after treatment, including the many novel drug, radiation, and radionuclide therapies being developed at Memorial. At SKI, an ideal setting for such an instrument, the microSPECT will be an invaluable adjunct to the rapidly expanding small-animal imaging program.